Constructing twin two-span bridges over two busy roads and railroad tracks in Lebanon, Pennsylvania, presented challenges. But city officials also wanted the aesthetics to match the original brick patterns and colors found throughout the historic town. To achieve this, precast concrete structural components were joined with architectural precast concrete panels to create a distinctive and functional design.
The bridges, which were created to alleviate congestion and provide safe crossings, feature six precast concrete box beams per span, each of which was approximately 73 feet long, with fascia panels hung from the outside beams on each side. Precast concrete wing walls, abutments and a concrete slab also were provided. Northeast Prestressed Products cast the structural components and subcontracted the architectural fascia panels to Architectural Precast Innovations Inc.
“We provided the engineering and connection details, and they produced them to the specs and delivered them to the site,” says Troy Jenkins, chief engineer at NPP. “There were a lot of aesthetic requirements that required close communication with the engineer, contractor and other precaster.” The fascia panels also were provided for the approach slabs on each side, using the same arched appearance but with filled-in arches that were painted a dark gray. Six 25-foot-wide arched panels clad each side of each end of the bridges, with two 73-foot arched panels used over the roadways.
The exterior beams on each side of both bridges were cast with recessed pockets into which projections on the architectural panels were set. The beams had to act compositely with the deck prior to the fascia-panel installation to carry the panels’ weight safely, according to Ben J. Wadsworth, then at Dewberry Engineers Inc., the structural engineer on the project.
To achieve this, the deck was constructed in two parts. The deck concrete was placed to the center of the exterior beams and cured. Then the fascia panels were installed and the rest of the deck was cast. Studded, stainless-steel plates were embedded into the recessed beam pockets to serve as vertical supports for the panels. Threaded inserts were cast into the beams, while slotted inserts with vertical adjustments were cast into the panels. Stainless-steel bolts and bent plates then connected the two pieces.
The panels’ design was decided on after a series of public meetings to discuss bridge location and appearance, Jenkins notes. The panels feature a faux-stone design that was cast into the gray-tone panels using a formliner. Once erected, an artist painted the individual bricks in various shades to replicate the look of actual mottled, older brick. The panels provide the shape of extended arches spanning the roadways.
The project was completed while the railroad remained active, requiring stoppages every hour or so to allow the trains to move through. “Everything moved very smoothly on the project,” says Jenkins.